If we look at the number of people who watched Batman Begins and Superman Returns then they are comparable...

It’s too bad movie popularity isn’t measured in the same way as books or music – that is, number of “units” (copies or tickets) sold. In this way, you’d know both absolute and relative popularity (an apples-to-apples comparison). What this info wouldn’t tell you is whether the movie was profitable. But even with gross $ figures available, gauging profitability is a very rough guess anyway.